Dems Reportedly Angry That Progressives Are Pushing Them to Act Like an Opposition Party.
(www.commondreams.org)
I disagree, or perhaps it depends on how you look at it. If a small, vocal minority in an overall larger group begin to push policies/opinions consistently that are not shared by the overall larger group, you could argue the values of the small and larger group no longer completely align. If the smaller group continues even after being made aware those policies/opinions aren't going to fly, one could argue they are now separate groups. I suppose it depends on how far their values have grown apart from each other.
I'm not necessarily saying that is what is happening here, but it's no secret progressives aren't happy with the democratic party establishment. Starting your own party might be best.